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Chapter 5 OPPORTUNITIES IN PARTICULAR TECHNOLOGIES SUMMARY This chapter describes opportunities for research and development where advances in electrochemical devices and processes will probably have a significant economic impact in the near term (less than 10 years). Both new and traditional industries are considered. The current status and needs for research and technology development, along with some institutional issues, are examined for Batteries and fuel cells: Technical requirements are documented for advanced applications in ground-based vehicles, space and central electric utility systems, communication systems, medical applications, and weapons; associated research and development topics are summarized. Biomedical science and health care: Electrochemical processes characteristic of living systems are reviewed, including such aspects as applications based on neuroscience, enzyme biocatalysis, adhesion and cell fusion, and electrophoresis. Coatings and films: Most paints and coatings degrade by a photoelectrochemical mechanism. Applications are summarized that include protective coatings for automobiles, encapsulants for microelectronic devices, electrocatalysts, and microencapsulation techniques for controlled release of electroactive components. Electrochemical corrosion: A framework of opportunities is presented with respect to corrosion research and engineering, dissemination of information, and new control technology to reduce corrosion losses. . Electrochemical surface processing: Research and development underlying new monolithic and composite materials, coatings, electroplating and etching, and microelectronic devices, among others, are highlighted. Manufacturing and waste utilization: Current applications and emerging technologies are reviewed, and dominant economic considerations are noted for electrolytic processes, electro-organic synthesis, 41

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42 coproduction of metals and anodic products, and specific applications such as vehicles, electric power, and waste utilization. Membranes: Directions are outlined to achieve greater membrane stability and molecular transport and in turn to permit wider use of energy-efficient and economically attractive membrane technology in biotechnology, health care, and chemical synthesis. Microelectronics: Electrochemical phenomena are essential in the manufacture of electronic and photonic systems as well as responsible for the quality and reliability of such systems. Applications and research are outlined in areas that include manufacture of microcircuits, interconnecting networks, lightwave communication devices, parallel processors, content-addressable memories, and nerve-electronic interfaces. Sensors: Key technical problems involve materials and fabrication methods for both gas-and liquid sensors; opportunities for utilizing advanced microelectronics and membrane technologies are suggested for applications in 'environmental, industrial, and clinical systems, including in vivo monitoring of drug delivery systems. Electrochemical science and engineering is moving extremely rapidly in areas of advanced energy conversion devices, microelectronics, and sensors. These technologies have significant market growth potential, and international competition is keen. Greater support from both federal and industrial sources would have a major impact in these areas. BATTERIES AND FUEL CELLS The current and emerging applications for batteries and fuel cells are numerous and highly varied (1-4~. These chemical sources of electrical energy are absolutely essential for life in today's world. A sampling of current applications includes portable electric power for a wide range of civilian, industrial, military, and aerospace applications such as flashlights, radios, tools, medical devices (heart pacemakers, drug delivery systems), weapons, communication equipment, alarms, signals, and satellite power in space. All of the world's telephones operate with batteries as standby power sources. Standby power, emergency power, and uninterruptable power are provided by batteries for high-priority systems such as hospitals computers, and military weapons installa ~ . lions. Motive power is provided by batteries for hundreds of thousands of specialty vehicles such as forklift trucks, personnel carriers, air- port utility vehicles, submarines, torpedoes, and drone aircraft. New battery systems are being developed with far greater specific power and specific energy than realized in conventional batteries (Figure 5-1~.

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200 100 ~0 SPECIFIC 60 POWER (W/kg) 40 30 20 Current _~__ Projected LiAl/FeS . Ii`,Si/FoS2 Chevette (1.4 liter) ~'A Zn/ NiOOH ~ ~ ~ ~ rVa/S _ ~`~- ~ ~/ Acceleration (Peak) ~ ------- `---r'y--------------- %~\ \~t -- - --^\---`\ ~\ 1 ~ ~ ~ 1 /` ~ ~ Pb/PbO2 \ ~ ~ ~ 1 1 . ... ~ . 10 . . t --i; Uman {AV~ ) , . .. .. . .. I I I I I l I I l! . 11 &., . , .. 1 1 1 1 .. 1 10 20 30 40 60 80100 200 300400 600 8001000 SPECIFIC ENERGY (W.h/kg) FIGURE 5-1 Specific energy versus specific power for several batteries under development, compared to the Pb-PbO2 battery. Note that high specific power and high specific energy are offered by some of the new batteries. Emerging applications for fuel cells and batteries are oriented toward higher performance and longer life. In the near term (within a decade), advanced electrochemical power sources will be available to act as the principal motive power source on a commercial basis for delivery vans, buses, and other fleet vehicles. In the far term (more than a decade away) these types of power sources will become available for higher-performance automobiles, rail vehicles, high-performance submarines, ships, and perhaps aircraft. Stationary energy storage applications include storage in electric utility networks (near-term availability), wind-powered electric systems (near-term), and solar-electric systems (far-term). Fuel cells (Figures 5-2 and 5-3) are strong candidates in the far term for high-efficiency (greater than 50 percent) commercial electric utility power generation and stand-alone power generation for shopping centers, hospitals, military installations, and industry, as well as for remote power generation in developing countries. Also, fuel-cell-powered vehicles of all types are a far-term possibility. At present there is an increased interest in ultrahigh-performance electrochemical systems for defense and space applications. Some of these systems could find application within the next decade. New high-performance miniature batteries are in demand for medical applications, including mobile heart-pump systems, drug-delivery

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44 H2 H2O - 3- _ , ~ = =: ~ an-' - = == ~9 . -=W ---~ L ~ =-=: .. ~ _ ~ ~ ~ ~- Air I Electrolyte l H2 Anode 2 2 2 O2 Cathode H2O N2, H2O FIGURE 5-2 Schematic cross section of a hydrogen-oxygen fuel cell, the heart of fuel cell systems. Such systems may be a major power source for electric utilities and electric vehicles. systems, and electrically powered prosthetic devices of various types. A number of these medical applications will be fulfilled within the next several years. The performance capabilities required of batteries and fuel cells vary according to the type of application. Some sample requirements are given in Tables 5-1 and 5-2. There are a number of barriers to achieving the requirements for various battery and fuel-cell applications. In general, improvements are needed in the areas of initial cost, lifetime, and performance.

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45 1orooo 3000 2000 u' a) U1 1000 ~ BOG . _ ~ 600 cn , 400 o a) 200 100 1 1 20 . ; ~40V \~\ 3.0 Lit 2.0 \\\ ZniAir~Li/~\ Li4Si/FeS2t Li/Fe \\\ \/Ai e:Na/S~ <~Na/SbC13 Li4si/Fcse~LiAllFes2\ \ \ LiAI/F~ 6~ In/NiOOH \\\ \ \ \ Nags \ \ Cd/Ag2O2- Fe/NiOOH \ \ \ Zn/HgO \ \ \ \ \ \ Cd/NiOOH \ \ 1 1 1 - - ~\\~ 1 ~ 1 \1 ~ N~ 1360 100 Equivalent Weight' g/equiv 104: a) llJ C' ._ _ Cal a) . En O 1o3 ~ 1 1 000 FIGURE 5-3 Theoretical specific energy for electrochemical cells. An opportunity exists for the development of systems that have the capability of storing 5 to 10 times more energy per unit weight than the Pb-PbO2 cell. More specific barriers to meeting the goals include the high cost of electrocatalysts and some porous electrodes; the prevention of corrosion of active and passive cell components; instabilities of porous electrode structures under long-term cycling; loss of electrocatalytic activity with time and use; susceptibility of electrolytes to oxidation and/or reduction by electrode reactants; inadequate conductivity of electrolytes for high-performance applications; inadequate membranes and separators (low chemical stability and conductivity); passivating film formation on electrodes; and lack of advanced electrode and cell designs for high-performance applications.

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46 TABLE 5-1 Performance Requirements for Batteries in Advanced Applications Specific Specific Battery Energy Power Efficiency Lifetime Cost Application (Wh/kg) (W/kg) (%) Cycles (years) ($/k\\'h) Autos and vans >70 >120 >60 >300 >3 <100 Stationary energy storage n/a n/a >70 >2000 >10 <100 Portable power for electronics >250* >2 n/a primary various 4000 Weapons (example) >100 >200 -- various various - NOTE: Efficiency (%) = percentage of theoretical efficiency. *The additional volumetric requirement of >0.6 Wh/cm3 is very important. TABLE 5-2 Performance Requirements~for Fuel Cells in Advanced Applications Specific Fuel Cell Power Efficiency Startup Cost Application (W/kg) (%) Time Lifetime ($/kW) Autos and vans 120 >30 <20 see Stationary utility n/a >40 <1 hr Weapons (example) >1000 >3 years <75 >10 years <1000 < 1 min < 1 hour Space power >100 >40 5000 hours - NOTE: Efficiency (%) = percentage of theoretical efficiency.

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47 A somewhat more general consideration of the battery and fuel-cell field reveals a number of generic problems that are important in numerous other electrochemical systems: The dimensional and morphological stability of porous electrode structures under operating conditions Chemical and physical control of electrocrystallization of metals and their solid discharge products Gas evolution at electrodes (H2 and/or O2 in aqueous systems) Electrocatalysis of O2 reduction and evolution Optimization of transport processes in porous electrode systems (gases, ions, electrons, solvents) Electrocatalysis of the oxidation of logistic fuels (hydrocarbons' reformer gas, methanol, coal) Suppression of passive film formation ~ Advanced methods for the design and optimization of electrodes, cells, and electrochemical systems Advanced methods for in situ study of electrochemical and chemical reactions in porous electrodes and immobilized electrolytes A plan for a more vigorous electrochemical R&D program (at a funding level at 2 to 3 times the present value) would, for research, enhance the funding and staff of existing programs of electrochemical research and focus added effort on the generic problems discussed here. For development, the plan would establish initiatives (described in Chapter 4) for each of the systems undergoing development berg., Na-S, Zn-Br2, Li-FeS2, H2-M2CO3-air, H2-ZrO2-air). BIOMEDICAL SCIENCE AND HEALTH CARE The origin of electric potentials in biological systems arises from the existence of free ions, ionized molecular groups, or electrically polarized biomolecules. In addition, electrical potentials accompany charge transfer processes during the reaction of biologically active systems. Although many processes that occur in biological systems lie outside the scope of this report, and although advances in these areas are likely to be made in a wide variety of disciplines, there are some key areas where electrochemical phenomena play a significant role. For example, the processes characteristic of living systems, such as active transport and secretory processes, photosynthesis, sensory and energy transduction, conduction and transmission of impulses, motility, and reproduction, are all based on interactions between ions, poly- electrolytes (proteins, DNA), or charged membranes containing enzymes and ion-selective channels. The units of these biological structures

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48 are charged, and their interactions involve electrical forces. An understanding' of life processes may thus be greatly aided by collaboration with individuals who possess a thorough grounding in electrochemical concepts and techniques. Such knowledge is also indispensable for developing ways of utilizing information about biological processes for industrial or medical applications (5~. The five examples that follow are illustrative but not inclusive of all areas where electrochemical phenomena represent an essential component. Mechanism of Enzyme Catalysis It is possible to carry out investigations of the electrochemical properties of proteins and enzymes in biological oxidation-reduction reactions in the native state. Highly significant is the fact that there is sometimes direct exchange of electrons between the protein molecule's active center and the electrode. The thermodynamics of the redox centers have been evaluated electrochemically with the use of indirect coulometric titration. The mechanisms of such electron transfer reactions, however, are not always obvious. Primarily, the role of the protein surface, and hence the pathway of electron transfer from the electrode to the redox center, is not well understood. Understanding of such phenomena will be quite valuable in resolving more difficult questions on the mechanism of electron transfer between redox centers when those centers are not directly accessible to an electrode. Model studies are needed for dioxygen and dinitrogen metabolism, cytochrome P-450, neuroactive substances, and redox chemistry of sulfur and selenium.' The use of complementary methods such as surface-enhanced Raman spectroscopy to probe interracial interactions or proteins on electrodes would represent an important contribution. The technological incentive for this work arises from the possibility of such electrodes serving as energy converters or for highly specific electro-organic synthesis. Neuroscience Proteins are major components in dendritic nerve membranes and may exhibit electroactivity i.e., the characteristic of being switched between two states of differing ionic conductivities. Such electro- activity is interesting because the electricity of the nerve impulse, the unitary basis of information encoding in neural systems, is generated in the dendritic membrane, which is composed of electro- chemically active proteins in a lipid bilayer. Thus' by interacting with neuroscientists in the investigation of neural information coders), electrochemists may make fundamental contributions to the molecular elucidation of the human brain and the nervous systems of other major animal species (6~.

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49 Technological applications emerging from such efforts include energy-transduction and -amplifying devices, information encoding devices for artificial intelligence systems, in vitro devices for sensing oxygen and pharmacological agents with membrane-immobilized proteins, and interface devices for organ or whole-body chemotherapy by metered drug release. These key scientific advances are needed in this area: Understanding of how complex ligands (e.g., messengers, drugs) affect selectivity and sensitivity of ionic permeabilities of protein membranes, films, or lamina Improved film prototypes, such as conducting polymers involving polypeptides, which might represent improved hosts for electroactive protein insertion, as well as the characterization of a larger number and variety of such proteins in order to improve knowledge of structure- activity relationships, including the contribution of the protein to the permeability-regulating capabilities of the laden film or membrane Better understanding of deterioration of ionic permeability, usually associated with unwanted protein adsorption, in order to to design synthetic systems that retain for practical periods their desired capabilities Cell Fusion Cell-to-cell fusion can be achieved with the aid of electrical stimulation (7-10~. Several techniques have been demonstrated in which an electric field is applied for a short duration to point- adhering (or agglutinated) cells, upon which fusion is immediately induced. The fusion may be achieved by a single DC pulse, by a series of pulses, or by gentle AC dielectrophoresis of a cell suspension. Electrofusion has been successful in all types of cells tested to date, including microbe and plant protoplasts, mammalian cells, and sea urchin ova. One can (a) fuse unlike cells to create hybrid cells; (b) fuse like cells to form larger entities such as giant cells 100 to 1000 times the volume of individual unit cells; and (c) help drive external objects or chemical agents such as DNA into cells. The mechanism of fusion is not understood. It is known that when application of an external electric field causes the potential difference across the separating membrane to reach a certain threshold value, the membrane becomes reversibly transformed from the rest state to a fusion-susceptible state, particularly in the contact zone between adjacent cells. The membrane excitation in a broad sense is observed

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50 usually in milliseconds in animal cells and in seconds in plant cells. In the fusion-susceptible state, the cell membrane or lipid bilayer becomes more permeable to ions and macromolecules. ~ In addition, the emergence of a protein-free domain occurs by lateral movement of proteins away from the contact zone of the membranes between two cells. The reversible electroporation of membranes at the contact zone leads eventually to fusion. The electrofusion technique is a significant new tool for research and production of controlled systems in the life sciences. The study of electric-field-induced membrane and cell phenomena on a molecular level will contribute to fundamental understanding both of cell-to-cell fusion and of membrane structure and function. In Vivo Monitoring In vivo measurements of chemical substances can be used to provide a great deal of information concerning the regulation, metabolism, and actions of various substances inside living organisms. Chemical sensors based on electrochemical techniques are well suited for this applica- tion, because they can be miniaturized so that minimal damage is caused to the tissue to be probed. These electrochemical sensors can be used to measure the distribution and concentration fluctuations of endogenous substances or to study events in vivo such as drug partitioning between different phases. Ton-selective electrodes with tip diameters in the range of 0.5 to lO,um have been developed for ions such as potassium, calcium, and chloride, and these have been used to study the distribution of these ions in both the extra- and intra-cellular fluid. These electrodes are used in the potentiometric mode, and the specificity is established by using a selective membrane that is only permeable to the ion of interest. Voltammetric techniques have also been useful for in viva measurements; the most widely used is the oxygen electrode, which incorporates a polymer film that is only permeable to oxygen. Electrode surfaces that have been properly modified with bioreactive layers (enzyme, antibody, receptor) can provide access to the in vivo investigation of biologically significant materials. Such devices offer simplicity, low cost, miniaturization, automation and high sensitivity. Key research areas include Discovery of nolv,mer coatings that- maintain sensitivity. promote O _ _ _ _ _ ~ _ _ _ _ _ _ _ _ selectivity, protect the electrode from the biological fluid, and provide a biocompatible surface to the measured system Development of new and improved immobilized enzymes to increase the scone of substances that can be detected by such techniques

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51 Investigation of in viva environments with the use of very fast electrochemical techniques for the elucidation of biologically significant kinetic processes Electrophoresis Electrophoresis is defined as the transport of electrically charged particles in liquid media under the influence of a DC electrical field. In these techniques, ionic constituents separate either as a function of their different rates of migration or by approaching zero mobility at different locations in an equilibrium gradient (11~. One of the most important applications of this spectrum of techniques is the separation and analysis of complex mixtures of biological origin in particular peptides, proteins, and nucleic acids. At present, two- dimensional gel electrophoresis, combined with sophisticated computer image analysis, is capable of resolving several thousand proteins among the products of a given cell type (12~. The most important applications of electrophoresis are in molecular biology and medicine where, for example, the study of inherent variabilities of serum proteins has produced a new branch of genetics, and the discovery of hemoglobin variants in several anemias has introduced the notion of molecular diseases. Electrophoresis has also greatly facilitated sequencing of nucleic acids, the clinical diagnosis of protein dyscrasias, the measurement of isoenzyme distribution, and the classification of lipoproteinemias, among others. In analytical applications the fluid is entrapped in a matrix, and visualization of the electrophoresed one- and two-dimensional patterns is done by staining, biological assays, or autoradiography, while data analysis is typically performed by densitometry (11-13~. Large-scale electrophoretic chambers (14-16) are currently being investigated for fractionation and purification of pharmaceuticals and other fermentation products on an industrial scale. COATINGS AND FILMS The need to modify the electrochemical properties of electrode- solution interfaces has led to the development of a wide range of coatings. The industry that coating technology supports has multibillion-dollar annual sales and includes areas such as paints, enamels, electrodeposits, and conductive polymers. As a result of advances in the fields of surface modification, surface character- ization, and adhesion, a revolution is occurring in coating technology. In many cases it is now possible to design coatings having desired

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84 cation systems, the circuits are packaged in particularly expensive ceramic hermetically sealed packages. Packaging and encapsulation now constitutes 15 to 50 percent of the cost of microcircuits. If one adds the expense of careful exclusion of ions in the processing steps (use of deionized water, high-purity solvents, sodium-free reagents, etc.), the cost of this ignorance of surface electrolytic processes in micro- circuits is even higher. Encapsulants of integrated circuits were originally introduced to prevent mechanical damage and to slow down corrosion by reducing transport of oxygen and water to the corroding metals. Today it is recognized that encapsulants reduce corrosion by reacting with regions on the hydrated SiO2 surface, thus slowing the lateral transport of ions. Some encapsulants also act as ion traps. It is reasonable to expect that, if methods for quantitative measure- ment of the transport of ions in surface phases of semiconductors are developed, the way will open to the exploration of chemical and physical modification of these surface phases. The goal is to make these less conductive solid electrolytes-i.e., surface phases in which ion transport is reduced. Such modification is likely to reduce the cost of encap- sulation and packaging and increase the reliability of microcircuits. Reliability of Interconnecting Networks Multilevel interconnecting networks consist of layers of metal runners isolated from each other by a dielectric. At defined points, runners in different planes are electrically contacted by metal columns. The purpose of these three-dimensional networks is to carry electrical signals at high speed. Therefore, the resistance and capacitance of the interconnecting networks must be low. Low resistance in a dense network of conductors implies that the runners must be made of highly conductive metals such as copper. Low capacitance implies that the layer of the dielectric must be thick and that its dielectric constant must be low. Usually, the layers isolating the metal layers are polymers like polyimides. Because oxygen diffuses to the polymer- copper interface, the copper oxidizes. If complexing functions like carboxylic acids are formed upon oxidation of the polymer or are intrinsically present, they complex the copper cations, causing both gradual dissolution of the metal and a change in the electrical properties of the dielectric. Because multilayer interconnecting networks are an important element of advanced chips and parallel processors, it is essential that an understanding of the corrosion processes that affect their reliability be developed. Needed are methods to quantify metal corrosion and ion transport in polymers and means to identify electrochemically reliable metal-polymer systems.

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85 Electrochemistry of Highly Parallel Processors The production of future generations of highly parallel processors requires manufacturing processes of unprecedented stringency in yield and precision. These processors will have dimensions of 10 to 100 cm2 and will consist of approximately 104 VLSI chips, with each chip connected to every other chip by approximately 102 metal runners, accommodated in a three-dimensional network. Their design requires. as , .~ e , ~ seen In the previous section, ~n-depth understanding of the interracial electrochemistry between metals and dielectrics and of ion transport in channels of diminishing size that connect metal runners in different planes. Formation of the networks requires extreme control over the plating process so that all columns have precisely identical lengths and perfectly flat tops; nonidentical lengths or curved tops lead to defects in the three-dimensional structure. The most relevant areas of fundamental electrochemistry are modeling of microcells and interracial corrosion. Electrochemistry of Content-Addressable Memories Beyonc} the evolution of von Neumann computers lies the beginning of the science and technology of content-addressable memories now being experienced. These approach more closely the way the human mind works. They are more fault-tolerant and associative; i.e., they function with imprecisely defined information and with imperfect circuit elements and can relate information elements to each other. State-of-the-art associative memories are based on variable-resistance network "opens" and variable degrees of "shorts." The variable shorts can be generated electrochemically both in polymers and in inorganic materials e.g., by the reductive electrochemical diffusion of Na+ into WO3 films, which produces conductive tungsten bronzes, or by the oxidative diffusion of C1O4- into polyalkyl thiophene films, which produces a conductive polymer. Such circuit elements have already been made. The most relevant areas of fundamental electrochemistry are solid-state electrochemistry and the modeling of microcells. Electrochemistry of Nerve-Electronics Interfaces The electrochemistry of nerves has been the subject of several decades of study. Ion transport across cell walls is a key element in the functioning of nerve cells, and a network of nerves can be viewed as a set of electrochemical, membrane-containing microcells that are coupled by chemical messengers. Interfaces between nerves and

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86 microelectronic triggers that are crude by biological standards have already been implemented and are in limited use in rehabilitation. The modeling of coupled electrochemical microcelis, progress in capacitive biocompatible microelectrodes, and the creation of precisely tailored arrays of microelectrodes are particularly relevant to the coupling of microelectronics and nerves. SENSORS Electrochemical sensors have demonstrated their potential to provide sensitive, selective, reliable, robust, and inexpensive means for solving otherwise intractable problems of chemical analysis (72~. They have proved to be well suited for application to both gas phase and liquid phase problems, including clinical chemistry and research in the life sciences (73,74~. Some noteworthy devices include miniature sensors for real-time monitoring of oxygen partial pressure in high- temperature automobile exhausts, lightweight portable monitors for a variety of toxic gaseous species (e.g., carbon monoxide, nitric oxide, nitrogen dioxide, hydrogen sulfide), ion-selective electrodes for measurement of electrolytes in clinical applications (sodium, potassium, calcium, etc.), ultramicroelectrodes for in viva determination of glucose and of biologically active species, detectors for liquid chromatography of drugs used for neurological disorders and for therapeutic drug monitoring, and potentiometric sensors for quantification of low concentrations of electroactive species. With the exception of potentiometric sensors, no consistent pattern of federal support has existed. Recent advances in microelectronic fabrication techniques, in development of modified electrode surfaces and ion-selective membranes, and in availability of new materials give promise for development of new electrochemical sensors. For both gas and liquid sensors, the possibility of much higher sensitivity exists. Lower detection limits are possible for environmental, clinical, and general analysis situations. Sensors developed to date are primarily based on classical and relatively unsophisticated approaches. With newer methodologies and device designs, one may anticipate at least a ten-fold improvement in detection limits. Among the methods that have considerable promise but that are yet to be significantly exploited are pulse electrochemical techniques, impedance methods, flow-injection analysis, the use of nonaqueous solvents in the sensor, the combined use of chemometrics and multi- electrode measurements for analysis of complex mixtures, the use of ultramicroelectrodes in applications outside the clinical and biological areas, and rapid deaeration of flow systems.

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87 Electrochemical sensors are based on selective interracial charge generation and localized charge transport. Within the past decade, major advances have been made in recognizing basic principles that unite the wide variety of systems encountered in practice. From these principles and the working out of charge, potential, and composition Profiles. Prediction of the properties of materials for the design and , , ~ . . ~ . ~ ~ ~ ~ . ~ ~ ~ ~. construction of new sensors has proceeded at an increasingly rapla rate. Key scientific challenges include the design of new molecules and substrates that possess the high transport selectivity required for new and improved sensors. The discovery and molecular characterization of new sensing elements will include surfaces modified with specific electrocatalysts and/or enzymes, ion-specific membranes, fast ion- conducting ceramics and glasses, conducting polymers, and semiconductor materials. The use of surface analytical techniques to probe the molecular details of the sensing mechanism of these materials will contribute to improved sensitivity i.e., reduced interference by other species. Closely related is the problem of sensor design for use in very low concentrations of species. Theoretical characterization of transport of sensed materials to and from the sensor interface must advance significantly to design reliable and reproducible sensors and to predict their responses in the transient and steady states. The invention of new devices would be aided significantly by transposing the principles of potential- and current-generating sensors to related field-effect devices, by capitalizing on improved knowledge of permselectivity in polymer films, and by exploring more deeply the principles of charge cancellation reactions for immunological applications. Invention of new manufacturing methods based on the microelectronics industry, coupled with new sensing materials and methods of detection, would represent a significant advance. For example, new sensors based on redundant arrays of microsensing devices may be key to low-cost reliability, which is essential to many applications. A significant barrier to developing improved sensors is the lack of focus for support of fundamental studies and the inadequate marshalling of multidisciplinary skills for development efforts. Much sensor development now occurs in connection with health science needs, defense needs, or the requirements of other mission-oriented agencies. Without a focus of support, it is currently difficult to undertake fundamental, systematic studies that would explore a new generation of sensing techniques and materials. Sensor technology is multidisciplinary, both in the assembly and characterization of the sensing element and in the fitting of that element into the specific system in the field. Manufacturers of instruments often do not have specialist teams with adequate breadth to develop novel techniques into commercial devices. As a consequence, there are missed opportunities in the conception of

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88 new methods as well as poor transfer to the marketplace of those concepts that do arise. In general there appear to be no generic problems that are inherent to the development and fabrication of vastly improved electrochemical sensors. The environment in which a sensor operates may generate materials problems (such as in blood or at high temperature or pressure), but these are not appreciably different from those existing for other instruments and devices exposed to the same environment. It is unlikely that more sophisticated sensors would give rise to intract- able materials or manufacturing problems. The present role of the federal government in support of sensor science and technology is unfocused. There is no clearly evident federal funding agency where a fundamental sensor proposal might attract funding without being directly linked to a specific mission-oriented problem. Improved federal sponsorship of fundamental investigations aimed at developing principles of advanced sensors would play a major role in promoting technological progress. The commercialization of new and improved sensors by U.S. manufacturing firms represents a very significant and strategic economic benefit. Research areas that hold high promise for advancing technological growth include ~ Enhancing sensor selectivity by discovery and molecular characterization of new and improved sensing elements Invention of new fabrication methods, based on microdevice technology, to improve reliability, reproducibility, and cost REFERENCES 1. Committee on Battery Materials Technology. Assessment of Research Needs for Advanced Battery Systems. National Materials Advisory Board, NMAB-390. Washington, D.C.: National Academy Press, 1982. Committee on Fuel Cell Materials Technology in Vehicular Propulsion. Fuel Cell Materials Technology in Vehicular Propulsion. National Materials Advisory Board, NMAB-411. Washington, D.C.: National Academy Press, 1983 . Extended Abstracts: Seventh Battery and Electrochemical Contractors' Conference. U.S. Department of Energy, CONF-851146-Absts, Nov. 1985.

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89 Assessment of Research Needs for Advanced Fuel Ceils. U.S. Department of Energy, July 1985. 5. Srinivason, S., Yu. A. Chizmadzhev, I. O'M. Prockris, B. E. Conway, and E. Yeager, eds. Comprehensive Treatise of Electrochemistry, Vol. 10: Bioelectrochemistry. New York: Plenum Press, 1985. 6. Senda, M., H. Morikawa, and J. Takeda. Seibtsu Butsuri. Biophysics, 22:14, 1982. 7. Norris, Dale M. Anti-Feeding Compounds. Chemistry of Plant Protection I. Berlin: Springer-Veriag, 1985. 8. Zimmerman, U. Electric field mediated fusion and related electrical phenomena. Biochim. Biophys. Acta, 694:227, 1982. 9. Berg, Herman, Hurt Audsten, Eckhard Bauer, Walter Forester, Hans Egan Jacob, Peter Muelig, and Herbert Weber. Possibilities of cell fusion and transformation by electrostimulation. Bioelectrochemistry and Bioenergetics, 12(1 -2~: 119, 1984. 10. PohI, Herbert A., K. Pollock, and H. Rivera. The electrofusion of cells. Int. I. Quantum Chem., Quantum Biology Symposium, 11:327, 1984. 11. Deyl, Z. Electrophoresis. A Survey of Techniques and Applications. P. G. Righetti, C. J. van Ossand, and J. W. Vanderhoff, eds. Amsterdam: Elsevier, 1979. 12. Cells, J. E., and R. Bravo. Methods and Applications of Two-Dimensional Gel Electrophoresis of Proteins. New York: Academic Press, 1984. ; 13. Righetti, P. G. Isoelectric Focusing: Theory, Methodology and Applications. Amsterdam: Elsevier Biomedical, 1983. 14. Hannig, Kurt. New aspects in preparative and analytic continuous free-flow cell electrophoresis. GIT Lab.-Med., 3~5~:235, 1982. 15. Wagner, H., and R. Kessler. GIT Lab.-Med., 7:~30), 1984. 16. Bier, M., N. B. Egen, T. T. Allgyer, G. E. Twitty, and R. A. Mosher. Peptides: Structure and Biological Function. E. Gross and I. Meienhofer, eds. Rockford, Illinois: Pierce Chemical Co., 1979, pp. 35-48. 17. Uhlig, H. H. 1984. The Corrosion Handbook. New York: John Wiley & Sons,

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